Preparation of high assay decabromodiphenyl oxide

ABSTRACT

A process is described for producing a reaction-derived decabromodiphenyl oxide product of high purity. In a continuous bromination process, partially brominated diphenyl oxide and coproduct hydrogen bromide are formed by bringing together elemental bromine and diphenyl oxide continuously in a first reaction zone. The partially brominated diphenyl oxide formed has an average of about 2-6 bromine atoms per molecule. The vapor phase and the partially brominated diphenyl oxide are removed continuously from the first reaction zone as separate entities. Then, or after storage, partially brominated diphenyl oxide is fed to a second reaction zone. This zone contains a refluxing reaction mixture comprising (i) an excess of bromine and (ii) a catalytic quantity of Lewis acid bromination catalyst. As the reaction in this zone is taking place, hydrogen bromide coproduct is removed therefrom in a sufficient amount to form a reaction-derived decabromodiphenyl oxide product of high purity.

REFERENCE TO RELATED APPLICATION

This application claims the benefit and priority of U.S. ProvisionalApplication No. 60/823,817, filed Aug. 29, 2006, the disclosure of whichis incorporated herein by reference.

TECHNICAL FIELD

This invention relates to improvements in the preparation ofdecabromodiphenyl oxide products, and more particularly to processtechnology for producing decabromodiphenyl oxide of high purity.

BACKGROUND

Decabromodiphenyl oxide (DBDPO) is a time-proven flame retardant for usein many flammable macromolecular materials, e.g. thermoplastics,thermosets, cellulosic materials and back coating applications.

The prior art describes many different processes for producing DBDPO.Despite these prior efforts, apparently it was not possible to producehigh purity DBDPO (e.g., DBDPO of a purity of greater than 90%),especially on an industrial scale, unless recrystallization or likeexpensive purification procedures are utilized.

DBDPO is presently sold as a powder derived from the bromination ofdiphenyl oxide (DPO) or a partially brominated DPO containing an averageof about 0.7 bromine atom per molecule of DPO. Such bromination isconducted in excess bromine and in the presence of a brominationcatalyst, usually AlCl₃. The operation is typically conducted at 177° F.(ca. 80.5° C.) with a 2-3 hour feed time. The powdered products are not100% DBDPO, but rather are mixtures that contain up to about 98% DBDPOand about 1.5%, or a little more, of nonabromodiphenyl oxide co-product.As a partially brominated product, this amount of nonabromodiphenyloxide is considered problematic by some environmental entities.

It would therefore be desirable to provide process technology, making itpossible to prepare highly pure DBDPO on an industrial scale withimproved plant throughput. Besides eliminating the need for use of suchpurification procedures as recrystallization or chromatographicpurification, it would be highly desirable to be able to produce highpurity DBDPO with increased plant throughput. Highly desirable productswould be products comprising (i) at least 99% of DBDPO and (ii)nonabromodiphenyl oxide in an amount not exceeding 0.5%, preferably notexceeding 0.3%, and still more preferably, not exceeding about 0.1%. Itwould be especially desirable if one could produce DBDPO productscomprising (i) at least 99.5% of DBDPO and (ii) nonabromodiphenyl oxidein an amount not exceeding 0.5%, preferably not exceeding 0.3%, andstill more preferably, not exceeding about 0.1% on an industrial scalewith improved plant throughput for a plant of any given plant capacity.

BRIEF SUMMARY OF THE INVENTION

This invention provides improved industrially feasible processtechnology for producing DBDPO with improved plant throughput. Indeed,the process technology of this invention is deemed to enable formationof DBDPO products of greater than 99% purity comprising (i) at least99.5% of DBDPO and (ii) nonabromodiphenyl oxide in an amount notexceeding 0.5%, preferably not exceeding 0.3%, and still morepreferably, not exceeding about 0.1% on an industrial scale withimproved plant throughput for a plant of any given plant capacity. Andin all cases, the need for recrystallization, chromatographicpurification, or like expensive procedures is eliminated pursuant tothis invention.

In accordance with one embodiment of this invention, there is provided aprocess for producing a decabromodiphenyl oxide product of high purity,which process comprises:

-   -   A) (1) substantially continuously forming partially brominated        diphenyl oxide and coproduct hydrogen bromide by substantially        continuously bringing together elemental bromine and diphenyl        oxide in a first reaction zone so that a reaction mixture        containing partially brominated diphenyl oxide having an average        in the range of about 2 to about 6 bromine atoms per molecule is        formed, (2) substantially continuously removing a vapor phase        comprising coproduct hydrogen bromide from the first reaction        zone, and (3) substantially continuously withdrawing from the        first reaction zone a reaction product mixture comprising        partially brominated diphenyl oxide having in the range of about        2 to about 6 bromine atoms per molecule; and    -   B) feeding reaction product mixture formed in A) substantially        continuously into a second reaction zone containing a refluxing        reaction mixture comprising (i) an excess of bromine and (ii) a        catalytic quantity of Lewis acid bromination catalyst, and        substantially concurrently removing hydrogen bromide coproduct        from the second reaction zone in a sufficient amount to form a        reaction-derived decabromodiphenyl oxide product of high purity.        It will of course be understood and appreciated that the terms        “first” and “second” as applied to the above reaction zones is        merely to distinguish one from the other. In an actual plant        facility, for the practice of this invention, there may be        several reaction zones, the first of which, for example, could        be a reactor in which diphenyl oxide or bromine is produced.        Thus, the terms “first” and “second” do not constitute a        limitation as regards the position of a reaction zone in a        sequential arrangement of operations in a plant facility.

For the purposes of this invention, unless otherwise indicated, the %values given for DBDPO and nonabromodiphenyl oxide are to be understoodas being the area % values that are derived from gas chromatographyanalysis. A procedure for conducting such analyses is presentedhereinafter.

Another embodiment of this invention is a process of preparingreaction-derived decabromodiphenyl oxide of high purity, which processcomprises:

-   -   A) (1) substantially continuously forming partially brominated        diphenyl oxide and coproduct hydrogen bromide by substantially        continuously bringing together elemental bromine and diphenyl        oxide in a first reaction zone so that a reaction mixture        containing partially brominated diphenyl oxide having an average        in the range of about 2 to about 6 bromine atoms per molecule is        formed, (2) substantially continuously removing a vapor phase        comprising coproduct hydrogen bromide from the first reaction        zone, and (3) substantially continuously withdrawing from the        first reaction zone a reaction product mixture comprising        partially brominated diphenyl oxide having in the range of about        2 to about 6 bromine atoms per molecule; and    -   B) maintaining an inversely related time-temperature feed of        reaction product mixture formed in A) substantially continuously        into a second reaction zone containing a refluxing reaction        mixture comprising an excess of bromine containing Lewis acid        bromination catalyst, and substantially concurrently reducing        the concentration of hydrogen bromide coproduct dissolved in the        reaction mixture so that a reaction-derived decabromodiphenyl        oxide product of high purity is formed.        In this embodiment, the higher the temperature of the refluxing        reaction mixture, the shorter is the time of the feed (in a        batch process) or the shorter is the average residence time of        the reaction mixture in the second reaction zone (in a        continuous process). Likewise, the lower the temperature of the        refluxing reaction mixture, the longer is the time of the feed        (in a batch process) or the longer is the average residence time        of the reaction mixture in the second reaction zone (in a        continuous process).

As used herein including the claims:

1) The term “reaction-derived” means that the composition of the productis reaction determined and not the result of use of downstreampurification techniques, such as recrystallization or chromatography, orlike procedures that can affect the chemical composition of the product.Adding water or an aqueous base such as sodium hydroxide to the reactionmixture to inactivate the catalyst, and washing away of non-chemicallybound impurities by use of aqueous washes such as with water or diluteaqueous bases are not excluded by the term “reaction-derived”. In otherwords, the products are directly produced in the synthesis processwithout use of any subsequent procedure to remove or that removesnonabromodiphenyl oxide from decabromodiphenyl oxide.

2) The term “high purity” means that the reaction-derived DBDPO productcomprises more than 99% of DBDPO and nonabromodiphenyl oxide in anamount of less than 1% with, if any, a trace of octabromodiphenyl oxide.Preferably the process forms a reaction-derived product which comprises(i) at least 99.5% of DBDPO and (ii) nonabromodiphenyl oxide in anamount not exceeding 0.5%, preferably not exceeding 0.3%, and still morepreferably, not exceeding about 0.1%.

3) The terms “substantially continuously” and “substantially continuous”mean that the operation referred to is carried out on a totallycontinuous basis with no interruptions whatever or that the operationreferred to is interrupted one or more times as long as suchinterruptions are of short enough duration as not to affect in anysignificant way the end result of producing a reaction-derived DBDPOproduct of high purity.

4) The term “substantially concurrently reducing” as regards the amountof hydrogen bromide means that the reducing is taking place at exactlythe same time or at substantially the same time that the feeding istaking place. Likewise the term “substantially concurrently feeding”means that the feeding is taking place at exactly the same time or atsubstantially the same time that the reducing of the amount of hydrogenbromide is taking place. It is to be clearly understood that the feedingand the reducing of the amount of hydrogen bromide need not start at thesame moment in time. For example, there can be a time lag between thecommencement of the feed and the evolution of enough hydrogen bromide toinitiate the reducing of the amount thereof in the reactor. Likewise, ifand when the feeding is terminated, there can be a period of timethereafter during which the amount of hydrogen bromide in the reactorcan be reduced. In addition, it should be understood that the terms“substantially concurrently reducing” and “substantially concurrentlyfeeding” include one or more interruptions in such operations as long assuch interruptions are of short enough duration as not to affect in anysignificant way the end result of producing a reaction-derived DBDPOproduct of high purity.

The reaction product mixture formed in step A) can be stored untilneeded as feed in step B), or such reaction product mixture can bedirectly fed in to the second reaction zone pursuant to step B).Alternatively, a portion of the reaction product mixture formed in stepA) can be directly fed into the second reaction zone pursuant to step B)with the remainder of such reaction product mixture being stored forsubsequent use as feed to step B). The reaction product mixture formedin step A) can be a solids-free liquid phase reaction product mixture orit can be in the form of a solids-containing liquid phase reactionproduct mixture, such as a slurry.

In order to produce high purity reaction-derived DBDPO product, themixture fed in B) consists essentially of (i) elemental bromine and (ii)partially brominated diphenyl oxide. This means that such liquid phasemixture is either completely devoid of hydrogen bromide or contains anamount of hydrogen bromide that is sufficiently small as not to precludethe formation in step B) of a reaction-derived DBDPO product of highpurity.

The reaction in B) can be conducted as a batch process or as acontinuous process. In either case, the production rate in any givenplant can be increased over conventional prior art processes. Thus, inaccordance with another of the embodiments of this invention, there isprovided an improved batch process. This process comprises a process asdescribed above wherein B) is conducted as a batch process wherein theamount of bromine present in the second reaction zone is at leastsufficient to maintain a stoichiometric excess in the second reactionzone, preferably without replenishment during the process. However,additional bromine can be fed into the second reaction zone beforeand/or during the feed of reaction product mixture formed in A).Pursuant to another of the embodiments of this invention, there isprovided an overall continuous process. In this overall continuousprocess, B) above is conducted as a continuous operation such that:

-   -   reaction product mixture formed in A) is substantially        continuously fed into the second reaction zone;    -   reaction mixture comprising decabromodiphenyl oxide product,        bromine, and catalyst substantially continuously exits from the        second reaction zone;    -   a separate vapor phase composed of hydrogen bromide and bromine        substantially continuously exits from the second reaction zone,        this vapor phase is passed through a condensing system so that        bromine is liquefied and returned to the second reaction zone        and hydrogen bromide passes through the condensing system and is        subsequently recovered, e.g., in a scrubber system containing,        say, water whereby hydrobromic acid is formed, or aqueous base        such as a NaOH or KOH whereby a metal bromide salt is formed.    -   Lewis acid bromination catalyst and additional bromine are        fed (i) periodically or continuously, and (ii) individually or        in admixture into the second reaction zone separately and apart        from the feed of reaction product mixture formed in A), and    -   the amount of additional Lewis acid bromination catalyst fed        into the second reaction zone is an amount that substantially        continuously maintains a catalytic amount of Lewis acid        bromination catalyst in the second reaction zone and the amount        of bromine fed into the second reaction zone is an amount that        substantially continuously maintains an excess of bromine in the        second reaction zone. Desirably, this excess is an excess in the        range of about 50 to about 150 mole percent more than the amount        theoretically required to perbrominate the partially brominated        diphenyl oxide.

The above and other embodiments and features of this invention willbecome still further apparent from the ensuing description and appendedclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a copy of the GC trace of the product formed in Example 1hereinafter.

FIG. 2 is a copy of the GC trace of the product formed in Example 2hereinafter.

FURTHER DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

As noted above the process technology of this invention comprises atleast steps A) and B).

Step A)

Step A) is conducted as a continuous process. Thus the rate of feed tothe first reaction zone and the rate of removal of the reaction productfrom the first reaction zone should be maintained such that the quantityof reaction mixture within the first reaction zone remains substantiallyconstant.

The reaction in A) can be conducted in the presence or absence of acatalyst. If a catalyst is used in A) it is important that the reactionproceeds to form a partially brominated diphenyl oxide product having anaverage in the range of about 2 to about 6, preferably in the range ofabout 3 to about 5, and more preferably about 4 bromine atoms permolecule. When conducting the reaction of step A) in the absence of acatalyst and at reflux temperatures in the range of about 57 to about60° C., partially brominated DBDPO having an average of about 4 bromineis typically formed. Preferably, the partially brominated DPO reactionproduct mixture formed in step A) is a solids-free solution. However, ifpartially brominated DPO reaction product mixtures formed in step A) inwhich the average number of bromine atoms per molecule is no more thanabout 6 bromine atoms per molecule do undergo precipitation formation,such reaction product mixture nevertheless can be used as feed in stepB), e.g., as a slurried feed.

It will be understood that the “partially brominated DPO” reactionproduct formed in step A) can contain some unbrominated DPO and/or somebrominated DPO having one bromine atom in the molecule. It will also beunderstood that the “partially brominated DPO” can be composed entirelyor substantially entirely of reaction product having the same number ofbromine atoms per molecule in the range of about 2 to about 6,preferably in the range of about 3 to about 5, and more preferably about4 bromine atoms per molecule.

To achieve the formation of partially brominated DPO, catalyst strength(if used), catalyst concentration (if catalyst is used), reactiontemperature, the pressure under which the reaction is conducted, and theaverage residence time in the reaction zone may all have an effect.

As noted above, step A) can be conducted in the absence of any addedcatalyst, or a suitable weak Lewis acid catalyst can be used. Any of avariety of such catalysts can be used to prepare partially brominatedDPO in step A). The catalysts used can be Lewis acids weaker thanaluminum chloride, aluminum bromide, ferric chloride, ferric bromide,gallium chloride, and gallium bromide. When using a catalyst, it isdesirable to use a known weaker Lewis acid such as antimony chloride,antimony bromide, zinc chloride, zinc bromide, zirconium tetrachloride,zirconium tetrabromide, titanium tetrachloride, titanium tetrabromide,or other known weaker Lewis acid.

In the absence of a catalyst, the reaction temperature used in A) isgenerally in the range of about 20 to about 60° C. When a catalyst isused the temperature should be somewhat less than used in the absence ofa catalyst, e.g., in the range of about 10 to about 50° C.

Increased reaction pressure tends to increase the extent of bromination.Nevertheless, pursuant to this invention, it is possible to operate atsuperatmospheric pressures in the range of about 5 to about 40 psig (ca.1.36×10⁵ to 3.77×10⁵ Pa) provided that the formation of precipitatingproduct solids having more than about 6 bromine atoms per molecule arenot formed in the reaction mixture, or at least the amount thereof iskept to a minimum. However, in carrying out step A) the pressure in thefirst reaction zone is preferably no more than autogenous pressure in aclosed reaction system, and more preferably, the pressure in the firstreaction zone is at substantially atmospheric pressure. It is alsopossible to operate at subatmospheric pressures.

The average residence time used in conducting A) above can vary.However, generally speaking, as long as the desired partially brominatedDPO is formed, the shorter the residence time, the better. Accordingly,the average residence times in the first reaction zone are typically inthe range of about 5 to about 90 minutes and preferably in the range ofabout 10 to about 60 minutes.

In the reaction of A), the first reaction zone can be in a partiallyfilled reactor having a vapor space or it can be conducted in a reactorfilled with liquid phase reaction mixture which is under autogenouspressure. In the former case, a vapor phase comprising hydrogen bromideis also formed in A) and in order to achieve high purity DBDPO, vaporphase comprising hydrogen bromide is substantially continuouslyseparated from the first reaction zone. In the latter case, the vaporphase is retained in the reaction mixture until release from the firstreaction zone. If necessary, steps should be taken to ensure that thefeed to the second reaction zone is devoid or substantially devoid ofhydrogen bromide, i.e., the lower the amount, if any, the better. By“substantially devoid” is meant that the amount of hydrogen bromidepresent in the feed to the second reaction zone is sufficiently low asnot to preclude the formation of reaction-derived DBDPO of high purity.

While various types of reaction equipment can be utilized in carryingout step A), use of at least one continuously stirred reactor, commonlyreferred to in the art as a CSTR, is preferred on the basis of economyand process efficiency. Operation in a CSTR which is devoid of addedLewis acid bromination catalyst is especially preferred.

The reaction of step A) can be conducted in various ways. Thus, the DPOcan be fed to bromine already present in the first reaction zone, or thebromine can be fed to DPO already present in the first reaction zone.Alternatively, the DPO and the bromine can be fed substantiallyconcurrently into the first reaction zone. Combinations of such feedtechniques can be used. If a catalyst is used it can be fed in admixturewith the bromine or in admixture with the DPO or the catalyst can be fedseparately as a concurrent feed. Combinations of such procedures canalso be used. In short, any suitable way of bringing the componentstogether in order to form the partially brominated DPO can be used.

Step B)

Among the principal features of step B) is that partially brominated DPOformed as in step A) is used as the feed to be brominated. Use of suchpartially brominated DPO feed enables removal of about 20 to about 60%or about 30 to about 50% or about 49% of the total HBr load in acontinuous operation in step A) while separately, and at the same timeif desired, conducting in step B) a second bromination reaction in thesecond reaction zone wherein feed formed in the step A) can bebrominated in step B) in a shorter reaction period (if a batch process)or with a shorter residence time (if a continuous process) and in eithercase, with a reduced total HBr load in step B). Another of the principalfeatures of step B) is that the combination of steps A) and B) producesa reaction-derived DBDPO product of high purity while retaining theability to accomplish this with higher plant throughput.

In the practice of this invention the processing disclosed in commonlyowned copending U.S. Application No. 60/823,811, filed on Aug. 29, 2006,and entitled “Preparation of High-Assay Decabromodiphenyl Oxide” isadapted for use herein in order to achieve preparation ofreaction-derived DBDPO product of high purity.

On the basis of studies conducted in our laboratories, one of the primedifficulties in producing high purity DBDPO is the existence of anequilibrium between nonabromodiphenyl oxide and decabromodiphenyl oxide.This equilibrium can be depicted as follows:

Br₉-DPO+Br₂

Br₁₀-DPO+HBr

As more fully described in the foregoing commonly owned application,prolonged feed of DPO and/or partially brominated DPO to refluxingbromine while substantially concurrently reducing hydrogen bromidecontent in the reactor enables a shift to the right in this equilibriumso that the amount of nonabromodiphenyl oxide is diminished and more ofthe desired decabromodiphenyl oxide forms and precipitates with lessnonabromodiphenyl oxide being coprecipitated within thedecabromodiphenyl oxide particles. It is also believed that if the DPOand/or partially brominated DPO is fed too rapidly, the precipitation ofat least one Brg-DPO isomer occurs so rapidly that the above equilibriumis not totally reached.

Accordingly, step B) is carried out in such a way as to maintain asubstantially continuous, coordinated time-temperature feed of partiallybrominated DPO feed formed as in step A) and thus having an average inthe range of about 2 to about 6 bromine atoms per molecule (preferablyan average in the range of about 3 to about 5 bromine atoms permolecule, and more preferably an average of about 4 bromine atoms permolecule) to a reactor containing a refluxing reaction mixturecomprising an excess of bromine containing Lewis acid brominationcatalyst, and substantially concurrently reducing the amount of hydrogenbromide coproduct present in the reactor so that a DBDPO productcontaining more than 99% of DBDPO is formed in the reactor.

A more particular process utilized herein as a preferred step B) processcomprises preparing reaction-derived decabromodiphenyl oxide of highpurity by feeding partially brominated diphenyl oxide into the secondreaction zone containing a refluxing reaction mixture comprising anexcess of bromine containing Lewis acid bromination catalyst. Becausepursuant to this invention the product of step A) is used as the feed,the time of the feeding is shortened and thus the overall plantthroughput is improved. Pursuant to this invention, a feed period in therange of about 2 to about 12 hours is used. While the feeding is takingplace, the content of hydrogen bromide present in the reactor issubstantially concurrently reduced so that a high puritydecabromodiphenyl oxide product is formed. The feed of the partiallybrominated diphenyl oxide is substantially continuous. However, it maybe possible to use a pulsed feed with suitable intervals of timeseparating the feeding periods. Such intervals of time separating thepulses of feed should be short enough as not to preclude the preparationof reaction-derived decabromodiphenyl oxide of high purity.

Generally speaking, from the viewpoint of productivity and plantthroughput, the shorter the feed period or residence time used, thebetter. But pursuant to this invention the feed period or residence timeused should be sufficiently long at the reaction temperature being usedto enable formation of a reaction-derived DBDPO product of high purity.

Therefore, depending on the temperature at which the bromination isoccurring, the feed of partially brominated DPO product(s) from step A)should occur during a period in the range of about 2 to about 12 hours,and preferably in the range of about 4 to about 10 hours, with suchperiod being long enough to reach the desired equilibrium state. Whenoperating at a plant scale this period of time in part represents acompromise between rate of reactor throughput and desire for as slow afeed as is practicable for achieving the desired product purity. Thus,the duration of the substantially continuous feed should be a period oftime that is prolonged yet consistent with achieving an economicallyacceptable plant throughput. The use of a slow feed is desirable as itprovides a longer period of time for a given quantity of DPO orpartially brominated DPO to reach the decabromodiphenyl oxide stagebefore significant precipitation of nonabromodiphenyl oxide encased indecabromodiphenyl oxide particles takes place.

In practicing a process of this invention it is important to minimizethe content of hydrogen bromide present in the reactor. Among variousways of achieving such minimization are the following:

A combination of vigorous refluxing of the bromine in the reactor,withdrawal of the hydrogen bromide vapor phase from the reactor, andefficient condensation of bromine vapors being withdrawn with thehydrogen bromide is desirable and is preferably utilized.

Use of a fractionation column to effectively separate as much HBr fromthe bromine in the column as feasible. In this way the bromine returningto the reactor carries less, if any, HBr back into the reactor. Thefractionation column can be a packed column or it can be free ofpacking, and should be designed to effect an efficient separation of HBrfrom bromine.

An inert gas purge of the reactor (e.g., with argon, neon, or preferablynitrogen) to carry away HBr is useful.

Use of bromine in the vapor state as a stripping gas. Besides carryingaway HBr, the use of bromine vapors is a way of introducing more heatinto the reactor and thereby contributing to more vigorous refluxingwithin the system.

Operation at atmospheric, subatmospheric or superatmospheric pressuresto enable a refluxing condition of the reaction mixture at the selectedprocess temperature.

Since the bromination is conducted in excess refluxing bromine, thereactor is of course equipped with a reflux condenser and preferably areflux fractionation column. This should be designed to return to thereaction as little HBr in the condensed bromine as is technically andeconomically feasible under the circumstances.

In all cases, the hydrogen bromide leaving the reaction system ispreferably recovered for use or sale. Recovery can be achieved by use ofa suitable scrubbing system using one or more aqueous liquid scrubberssuch as water, or dilute NaOH or KOH solution.

The relationship between bromination reaction temperature and pressureunder which the bromination in b) is being operated is worthy ofcomment. Ideally it is desirable to operate at as high a temperature aspossible and as low a pressure as possible to adequately reduce the HBrconcentration in the bromine as more HBr is removed from the reactor.Sampling a refluxing bromination reaction mixture of this type in orderto assay the percentage of HBr dissolved in the Br₂ at any given time isnot deemed feasible when using ordinary laboratory or plant equipment.Such sampling requires special equipment such as built-in stationaryprobes to periodically remove representative samples of the reactionmixture from the reactor. Thus when using ordinary plant equipment,operation at maximum temperature and minimum pressure is desirable as away of reducing the HBr concentration in the bromine. However,maintaining a high reaction temperature in such a reaction system is notas easy as it might appear. For one thing, considerable heat input isrequired to the reaction mixture, and this can impose limitations inexisting plant equipment. Consequently, in most cases it is desirablewhen operating on a commercial scale to conduct the reaction at a mildlyelevated pressure (e.g., in the range of about 5 to about 20 psig (ca.1.36×10⁵ to 2.39×10⁵ Pa)), and having the temperature high enough toeffect vigorous refluxing to thereby keep the HBr concentration in thebromine low as more HBr is removed from the reactor.

As noted above the process technology of this invention enables thepreparation of highly pure DBDPO products while at the same timeachieving improved plant throughput. For example, as seen from theExamples herein, DBDPO products having a purity of 100% as indicated byGC analysis have been prepared pursuant to this invention. Such productscan be said to be “reaction-derived” since they are reaction determinedand not the result of use of downstream purification techniques, such asrecrystallization, chromatography, or like procedures. In other words,the products are of high purity.

The partially brominated DPO can be fed as solids, but preferably thefeed is in molten form or as a solution in a solvent such as methylenebromide or bromoform. To prevent freeze up in the feed conduit, thepartially brominated DPO is desirably fed at a temperature that is atleast about 20 higher than the melting temperature of the particularpartially brominated DPO being fed.

Excess bromine is used in the Lewis acid catalyzed bromination reaction.Enough bromine should be present to provide in the range of about 4 toabout 12 moles of excess bromine over the amount required toperbrominate the partially brominated DPO.

As noted above, the refluxing temperature of bromine at atmospheric orslightly elevated pressures is in the range of about 57 to about 59° C.but when conducting B) at higher elevated pressures suitably highertemperatures should be used in order to maintain a vigorous refluxingcondition.

If desired, a suitable solvent can be included in the reaction mixturesof B). This can be advantageous in that one can have a higher reactiontemperature and possibly a lower HBr concentration in the brominethereby giving higher purity DBDPO. Among such solvents are methylenebromide and bromoform.

Various iron and/or aluminum Lewis acids can be added to the bromine toserve as the bromination catalyst. These include the metals themselvessuch as iron powder, aluminum foil, or aluminum powder, or mixturesthereof. Preferably use is made of such catalyst materials as, forexample, ferric chloride, ferric bromide, aluminum chloride, aluminumbromide, or mixtures of two or more such materials. More preferred arealuminum chloride and aluminum bromide with addition of aluminumchloride being more preferred from an economic standpoint. It ispossible that the makeup of the catalyst may change when contained in aliquid phase of refluxing bromine. For example, one or more of thechlorine atoms of the aluminum chloride may possibly be replaced bybromine atoms. Other chemical changes are also possible. The Lewis acidshould be employed in an amount sufficient to effect a catalytic effectupon the bromination reaction being conducted. Typically, the amount ofLewis acid used will be in the range of about 0.06 to about 2 wt %, andpreferably in the range of about 0.2 to about 0.7 wt % based on theweight of the bromine being used.

After all the partially brominated DPO is added, the reaction mixturecan be kept at reflux for a suitable period of time to ensure completionof the perbromination to DPDPO. A period of up to about one hour can beused. Generally speaking, the benefits of such post-reaction refluxingtend to offset by the prolongation of the overall operation, and thususe of such post reflux, though permissible, is not preferred.

Termination of the bromination reaction is typically effected bydeactivating the catalyst with water and/or an aqueous base such as asolution of sodium hydroxide or potassium hydroxide.

When conducting step B) on a continuous basis, after a suitable averageresidence time in the second reaction zone (e.g., in the range of about0.2 to about 3 hours), the reaction mixture is substantiallycontinuously withdrawn from the second reaction zone. The feed of thepartially brominated DPO can be a substantially continuous feed andbromine remaining associated with the partially brominated DPO productfrom step A) is co-fed therewith. Whether conducting the process on abatch basis or on a continuous basis it is desirable to substantiallycontinuously separate hydrogen bromide coproduct from the secondreaction zone. In addition, hydrogen bromide and liquid phase comprisingat least bromine and partially brominated diphenyl oxide substantiallycontinuously leave the first reaction zone.

Since hydrogen bromide is formed as a coproduct in both step A) and stepB), two scrubber systems can be employed, one receiving the hydrogenbromide effluent from step A) and the other receiving the hydrogenbromide effluent from step B). It is also possible to utilize onesufficiently large scrubbing system to receive both such effluentstreams of hydrogen bromide.

Various types of reaction equipment are known for conducting acontinuous reaction with continuous takeoff of a vapor phase componentfrom the reaction mixture and concurrently removing a liquid phasereaction product from the reactor. Typically, such reaction equipmentinvolves use of a refrigerated condenser system such as a refrigeratedcondenser column. Such columns can be packed columns or they can bedevoid of any packing. The vapor phase, which contains material that isto be returned in liquid form to the liquid phase for withdrawal fromthe reactor—in this case bromine—is condensed by use of refrigeration orother suitable means of cooling in the column. The remainder of thevapor phase which is not condensed—in this case hydrogen bromide—passesthrough the column as an effluent vapor and is recovered by introductioninto a suitable scrubbing system. If the scrubber contains water, thehydrogen bromide is converted to hydrobromic acid. If the scrubbercontains an aqueous base such as sodium hydroxide or potassiumhydroxide, the hydrogen bromide is converted to sodium bromide orpotassium bromide.

Gas Chromatographic Procedure

The gas chromatography is on a Hewlett-Packard 5890, series II, withHewlett-Packard model 3396 series II integrator, the software of whichis that installed with the integrator by the manufacturer. The gaschromatograph column used is an aluminum clad fused silica column, Code12 AQ5 HT5 (Serial number A132903) obtained from SGE Scientific, withfilm thickness of 0.15 micron. The program conditions are: initial starttemperature 250° C., ramped up to 300° C. at a rate of 5° C./min. Thecolumn head pressure is 10 psig (ca. 1.70×10⁵ Pa). The carrier gas ishelium. The injection port temperature is 275° C. and the flameionization temperature is 325° C. Samples are prepared by dissolving ca.0.1 g in 8-10 mL of dibromomethane. The injection size is 2.0microliters.

EXAMPLES

The practice of embodiments of the invention and advantages achievableby practice of the embodiments of the invention are illustrated in thefollowing Examples. These Examples, which serve as indications of thefeasibility of conducting at least step A) as a continuous operationfollowed by a step B) operation, are not intended to impose limitationson the overall scope of the invention. In these Examples, the first stepsimulates larger scale operation in a first reaction zone and step B)simulates larger scale operation is a second reaction zone.

Example 1 Step A: Formation of Partially Brominated Diphenyl Oxide

A 250-mL four-necked flask equipped with a mechanical stirrer, aglycol-cooled reflux condenser maintained at 0° C., an addition funnel,a thermometer with a temperature regulator and an ice-cold causticscrubber, was charged with 0.2 mol (34.0 g) of diphenyl oxide. Theaddition funnel was charged with bromine (1.2 mol, 192 g, approximately62 mL). Diphenyl oxide was heated to about 25° C. and stirred. Withstirring under nitrogen, bromine was now added, drop-wise, to thestirred diphenyloxide over a period of 55 minutes. The reaction mixturewas now heated and stirred at 45° C. for another 45 minutes. Thereaction mixture was now allowed to cool to room temperature. A dryingtube containing Drierite was installed on the condenser and the reactionmixture was stored overnight under nitrogen, for use the next day. Thetotal volume of this solution was approximately 67 mL.

Step B: Bromination of Partially Brominated Diphenyl Oxide Prepared inStep a, Above

A 1-L four-necked round bottom flask was equipped in a manner identicalto what was used in step A, above, except that the addition funnel wasalso equipped with a Teflon dip tube approximately 1/16″ in diameter andof sufficient length to reach well beneath the bromine surface forsub-surface feeding. Also, a vigreux column, approximately seven inchesin length and ½ in. in diameter, was installed on the reactor before thecondenser to provide additional fractionation of the liquid and vaporphases. The reactor was charged with bromine (3.97 moles, 635.5 g,approx. 2055 mL), followed by 3.4 g of anhydrous aluminum chloridecatalyst. The bromine/catalyst mixture was stirred and heated to 60° C.Partially brominated DPO (prepared before as described in step A,above), was now added, subsurface to bromine/catalyst at 60° C., over aperiod of about three hours and twenty three minutes. The reactionmixture was allowed to reflux at 60° C. for an additional three hours,while using the same dip tube to allow a slow nitrogen sweep through thereaction mixture. After the reflux time was over, the reaction mixturewas allowed to cool to room temperature. Water (250 mL) was now added todecompose the catalyst. Excess bromine was now removed by steamdistillation until the vapor temperature of 100° C. was reached. Theaqueous slurry of the product was allowed to cool to 40° C. Aqueoussodium hydroxide (50 wt. % solution) was now added until a pH of about9-10 was reached. The product was now filtered using a sintered glassfunnel and the cake was washed once with 200 mL of fresh water. The cakewas allowed to dry in air overnight. This gave a shiny crystalline solidpowder, weighing 185.9 grams. A GC analysis of the sample indicated theproduct to be 100 area % decabromodiphenyl oxide. Further analyticalanalysis of product sample using other protocols confirmeddecabromodiphenyl oxide purity of no less than about 99.7 area %.

Example 2 Step A: Formation of Partially Brominated Diphenyl Oxide

This step was performed in a manner identical to step A of example 1 asdescribed above, except that a 1-L round bottom flask was used. Thisflask was charged with 170 g (1.0 mol) of diphenyloxide to which a totalof 960 g (309.6 mL) of bromine was fed over a period of 1 hour andthirty eight minutes. The reaction temperature was maintained between25-35° C. during the addition, followed by a reflux at 50-58° C. forthirty minutes. This reaction mixture was stored overnight as describedin part A of Example 1, above. Total volume of this mixture wasapproximately 300 mL.

Step B: Bromination of Partially Brominated Diphenyl Oxide

This procedure was also performed in a manner identical to step B asdescribed for example 1 above. The equipment design was also identicalto the one used in step B, above. A brief description is as follows:

A 3-L round bottom flask was equipped with a mechanical stirrer, a 7in.×½ in. vigreux column to which was attached a glycol-cooled refluxcondenser, an addition funnel with a 1/16 in. Teflon dip tube forsub-surface feed, a thermometer with a temperature regulator and an icecold caustic scrubber. The reactor was charged with bromine (19.85 mol,3177.5 g, 1025 mL) and 17.0 g of anhydrous aluminum chloride catalyst.The bromine/catalyst mix was stirred under nitrogen and heated to 55° C.The addition funnel was charged with partially brominated DPO feed,prepared earlier as described in step A above. Partially brominated DPOwas then added, sub-surface, to the reactor containing bromine andcatalyst, over a period of 4.5 hours, at a temperature of 55-60° C. Thecontents were then heated at reflux for an additional two hours. Thereaction mixture was now cooled to room temperature and 250 mL of waterwas added to decompose the catalyst. An exotherm to 43° C. was observedupon water addition. After this another 950 mL of water (total=1200 mL)was added. The reaction mixture was now heated and excess bromine wasremoved by steam distillation until the vapor temperature of 100° C. wasreached. Heat was cut off and the contents were cooled to 30° C. Aqueouscaustic (50% aq. NaOH, 45.4 g) was added and stirred well. Filtered theproduct and the cake was washed with water (3×800 mL), followed bydrying in air overnight. This gave a light orange crystalline powder,weighing 952.3 g. A GC analysis of a small sample showed the product tobe 100 area % deca. This product was heated in an oven at 210° C. forsix hours to give 942.2 g of the finished product. Further analyticalanalysis of product sample using other protocols confirmeddecabromodiphenyl oxide purity of no less than about 99.7 area %.

DBDPO Products and Flame Retardant Usage

The DBDPO products formed in processes of this invention are white orslightly off-white in color. White color is advantageous as itsimplifies the end-user's task of insuring consistency of color in thearticles that are flame retarded with the DBDPO products.

The DBDPO products formed in the processes of this invention may be usedas flame retardants in formulations with virtually any flammablematerial. The material may be macromolecular, for example, a cellulosicmaterial or a polymer. Illustrative polymers are: olefin polymers,cross-linked and otherwise, for example homopolymers of ethylene,propylene, and butylene; copolymers of two or more of such alkenemonomers and copolymers of one or more of such alkene monomers and othercopolymerizable monomers, for example, ethylene/propylene copolymers,ethylene/ethyl acrylate copolymers and ethylene/propylene copolymers,ethylene/acrylate copolymers and ethylene/vinyl acetate copolymers;polymers of olefinically unsaturated monomers, for example, polystyrene,e.g. high impact polystyrene, and styrene copolymers, polyurethanes;polyamides; polyimides; polycarbonates; polyethers; acrylic resins;polyesters, especially poly(ethyleneterephthalate) andpoly(butyleneterephthalate); polyvinyl chloride; thermosets, forexample, epoxy resins; elastomers, for example, butadiene/styrenecopolymers and butadiene/acrylonitrile copolymers; terpolymers ofacrylonitrile, butadiene and styrene; natural rubber; butyl rubber andpolysiloxanes. The polymer may be, where appropriate, cross-linked bychemical means or by irradiation. The DBDPO products of this inventioncan be used in textile applications, such as in latex-based backcoatings.

The amount of a DBDPO product of this invention used in a formulationwill be that quantity needed to obtain the flame retardancy sought. Itwill be apparent to those skilled in the art that for all cases nosingle precise value for the proportion of the product in theformulation can be given, since this proportion will vary with theparticular flammable material, the presence of other additives and thedegree of flame retardancy sought in any given application. Further, theproportion necessary to achieve a given flame retardancy in a particularformulation will depend upon the shape of the article into which theformulation is to be made, for example, electrical insulation, tubing,electronic cabinets and film will each behave differently. In general,however, the formulation, and resultant product, may contain from about1 to about 30 wt %, preferably from about 5 to about 25 wt % DBDPOproduct of this invention. Master batches of polymer containing DBDPO,which are blended with additional amounts of substrate polymer,typically contain even higher concentrations of DBDPO, e.g., up to 50 wt% or more.

It is advantageous to use the DBDPO products of this invention incombination with antimony-based synergists, e.g., Sb₂O₃. Such use isconventionally practiced in all DBDPO applications. Generally, the DBDPOproducts of this invention will be used with the antimony basedsynergists in a weight ratio ranging from about 1:1 to 7:1, andpreferably of from about 2:1 to about 4:1.

Any of several conventional additives used in thermoplastic formulationsmay be used, in their respective conventional amounts, with the DBDPOproducts of this invention, e.g., plasticizers, antioxidants, fillers,pigments, UV stabilizers, etc.

Thermoplastic articles formed from formulations containing athermoplastic polymer and DBDPO product of this invention can beproduced conventionally, e.g., by injection molding, extrusion molding,compression molding, and the like. Blow molding may also be appropriatein certain cases.

Components referred to by chemical name or formula anywhere in thespecification or claims hereof, whether referred to in the singular orplural, are identified as they exist prior to coming into contact withanother substance referred to by chemical name or chemical type (e.g.,another component, a solvent, or etc.). It matters not what chemicalchanges, transformations and/or reactions, if any, take place in theresulting mixture or solution as such changes, transformations, and/orreactions are the natural result of bringing the specified componentstogether under the conditions called for pursuant to this disclosure.Thus the components are identified as ingredients to be brought togetherin connection with performing a desired operation or in forming adesired composition. Also, even though the claims hereinafter may referto substances, components and/or ingredients in the present tense(“comprises”, “is”, etc.), the reference is to the substance, componentor ingredient as it existed at the time just before it was firstcontacted, blended or mixed with one or more other substances,components and/or ingredients in accordance with the present disclosure.The fact that a substance, component or ingredient may have lost itsoriginal identity through a chemical reaction or transformation duringthe course of contacting, blending or mixing operations, if conducted inaccordance with this disclosure and with ordinary skill of a chemist, isthus of no practical concern.

Except as may be expressly otherwise indicated, the article “a” or “an”if and as used herein is not intended to limit, and should not beconstrued as limiting, a claim to a single element to which the articlerefers. Rather, the article “a” or “an” if and as used herein isintended to cover one or more such elements, unless the text expresslyindicates otherwise.

Each and every patent or publication referred to in any portion of thisspecification is incorporated in toto into this disclosure by reference,as if fully set forth herein.

1. A process for producing a reaction-derived decabromodiphenyl oxideproduct of high purity, which process comprises: A) (1) substantiallycontinuously forming partially brominated diphenyl oxide and coproducthydrogen bromide by substantially continuously bringing togetherelemental bromine and diphenyl oxide in a first reaction zone so that areaction mixture containing partially brominated diphenyl oxide havingan average in the range of about 2 to about 6 bromine atoms per moleculeis formed, (2) substantially continuously removing a vapor phasecomprising coproduct hydrogen bromide from the first reaction zone, and(3) substantially continuously withdrawing from the first reaction zonea reaction product mixture comprising partially brominated diphenyloxide having in the range of about 2 to about 6 bromine atoms permolecule; and B) feeding reaction product mixture formed in A)substantially continuously into a second reaction zone containing arefluxing reaction mixture comprising (i) an excess of bromine and (ii)a catalytic quantity of Lewis acid bromination catalyst, andsubstantially concurrently reducing the content of hydrogen bromidepresent in the reactor so that a reaction-derived decabromodiphenyloxide product of high purity is formed.
 2. A process as in claim 1wherein said reaction product mixture of (3) consists essentially of (i)elemental bromine and (ii) said partially brominated diphenyl oxide, andoptionally, (iii) weak Lewis acid bromination catalyst residue.
 3. Aprocess as in claim 1 wherein the reaction in A) is conducted in theabsence of any added catalyst.
 4. A process as in claim 1 wherein thereaction in A) is conducted in the presence of a weak Lewis acidbromination catalyst.
 5. A process as in claim 1 wherein said excess ofbromine is an excess of bromine in the range of about 50 to about 150mole percent of the amount required to perbrominate the partiallybrominated diphenyl oxide.
 6. A process as in claim 1 wherein B) isconducted as a batch process wherein the amount of bromine initiallypresent in said second reaction zone is at least sufficient to maintain,without replenishment during the process, an excess of bromine in therange of about 50 to about 150 mole percent of the amount required toperbrominate the partially brominated diphenyl oxide to be fed into saidsecond reaction zone.
 7. A process as in claim 1 wherein B) is conductedas a continuous operation such that in B): reaction product mixtureformed in A) is substantially continuously fed into the second reactionzone; reaction mixture comprising decabromodiphenyl oxide product,bromine, and catalyst substantially continuously exits from the secondreaction zone; a separate vapor phase composed of hydrogen bromide andbromine substantially continuously exits from the second reaction zone,and this vapor phase is passed through a condensing system so thatbromine is liquefied and returned to the second reaction zone; Lewisacid bromination catalyst and additional bromine are fed (i)periodically or continuously, and (ii) individually or in admixture intothe second reaction zone separately and apart from the feed of reactionproduct mixture formed in A); and the amount of additional Lewis acidbromination catalyst fed into the second reaction zone is an amount thatsubstantially continuously maintains a catalytic amount of Lewis acidbromination catalyst in the second reaction zone and the amount ofbromine fed into the second reaction zone is an amount thatsubstantially continuously maintains a stoichiometric excess of brominein the second reaction zone.
 8. A process as in claim 7 wherein saidstoichiometric excess is an excess of bromine in the range of about 50to about 150 mole percent of the amount required to perbrominate thepartially brominated diphenyl oxide being fed into said second reactionzone.
 9. A process as in claim 1 wherein said Lewis acid brominationcatalyst utilized in the second reaction zone is aluminum chloride oraluminum bromide, or both.
 10. A process as in claims 1 wherein saidreaction zone in A) is a continuously stirred tank reactor.
 11. Aprocess as in claim 1 wherein in B) an inversely relatedtime-temperature feed of reaction product mixture formed in A) into asecond reaction zone is maintained substantially continuously.